1. Technical Field
The present invention relates generally to a mobile communication systems and, in particular, to a system and method for controlling admission to a mobile communications system that provides reliable connectivity and maintains mobile user connectivity between mobile platforms and the communication network by automatically and transparently attempting to reconnect disrupted links.
2. Description of Related Art
Visions of the future allude to unprecedented availability of conveniences and services based on pervasive communication and computer technologies. The full realization of these ambitions requires ubiquitous, reliable communications for moving and stationary users on demand. At the core of these services is the reliable communication of voice, data, image, video, multi-media and control messages on networks that are designed to support a wide range of call types as well as users having different mobility characteristics. Significant trends in this regard are underway in essentially every industrialized country and increasingly, a vast communications infrastructure is becoming available which can grow to realize these aspirations.
As noted above, to provide services to mobile users comparable to those obtainable by fixed users via wireline facilities, appropriate attention must be paid to the peculiarities of mobile communications. Modem communications networks that support mobile platforms (pedestrians, vehicles, planes, trains, buses, etc.) often use many wireless gateways connected to a more or less fixed (backbone) network. The gateways, which are sometimes referred to as xe2x80x9ccellsxe2x80x9d xe2x80x9cbase stationsxe2x80x9d or xe2x80x9caccess points,xe2x80x9d allow tetherless links to nearby mobile platforms. Users within the coverage area of a gateway are said to be in the cell of that gateway. It is to be understood that the term xe2x80x9ccellxe2x80x9d is used herein in a broad generic sense and can mean gateway, sector, zone, macro-cell, micro-cell, etc. In wireless mobile environments, propagation conditions are often harsh due to multipath and fading, bandwidth is a severe constraint, while mobility support and call management add additional complexity. Furthermore, the network must support disparate call types whose distinct needs must be accommodated. Disparate call types may have different measures of quality and generally require different amounts and types of communications resources for acceptable service. Various resource types that may be needed for mobile communications include, for example, radio bandwidth (channels), buffer space at the gateways and in the backbone network, antenna beam steering system components (including tracking and steering processors at the gateways), call supervising processors at the gateways and in the backbone network, transmitted signal power at the gateways and at the mobile stations, access to control channels, and computational capability in various network components.
With conventional and future wireless and cellular systems that implement various call types (thereby requiring various resource types), appropriate attention must be paid to the peculiarities of mobile communications. In these environments, propagation conditions are often harsh due to multipath and fading, bandwidth is a severe constraint, while mobility support and call management add additional complexity. In addition, since tetherless or radio links to mobile platforms are of variable quality and change with time, they often fail. Accordingly, a lower layer admission control protocol and system that is capable of ameliorating the effects of such failures by maintaining a connection from an active mobile user to the network for the benefit of higher layer protocols is highly desirable.
The present invention is directed to a system and method for controlling admission to a mobile communications system, which allows mobile platforms each supporting any of a variety of call types, and each having differing mobility characteristics, to maintain connectivity to a backbone network in spite of unreliable radio links that occasionally fail. The present invention employs an admission protocol that provides automatic and user-transparent reconnection attempts for appropriate call sessions when an interruption of the link occurs. Further, a network that employs an admission protocol of the present invention may support a variety of different call types simultaneously, wherein access to network connectivity resources can be provided according to call session priority based on (for example, call session type, platform mobility, hand-off status, and user class (fee-for-service)) criteria. The admission control protocol provides support of suspended sessions and uses repeated reconnection attempts with priority access to network resources, and provides for hand-offs of suspended sessions to neighboring gateways as mobile terminals move throughout the service area.
In a network that employs an admission control protocol according to the present invention, voice calls, for example (or other time-sensitive stream traffic) may preempt resources of time-insensitive data calls, which result in suspended sessions that do not result in session failures. Priority access for hand-offs of active sessions with respect to new call sessions can also be accommodated. Mobile users that have some autonomy or who are perhaps exchanging time-insensitive data with a remote site can continue to function essentially undisturbed by link failures since the connectivity and reconnection procedures are managed by the network in a manner that is transparent to the end users. Mobile computing sessions and delay-insensitive data communications, for example, will be able to continue, largely unaware of link failures.
Since the present invention can be applied to admission control of sessions that are supported at each gateway, it is not necessary that a session that is admitted to a cell have dedicated access to resources. Thus, because some users may emit/receive data in bursts, other users who have been admitted to a cell can share the resources. This allows efficient resource use through rapid access and relinquishment of dedicated resources managed by the media access communications layer.
These and other aspects, features and advantages of the present invention will be described or become apparent from the following detailed description of preferred embodiments, which is to be read in connection with the accompanying drawings.